China's environment ministry is one of the four most embarrassing departments known to mankind, its minister has reportedly admitted.

In a startlingly blunt assessment of his five-year-old ministry, Zhou Shengxian was quoted by state media as saying: "I've heard that there are four major embarrassing departments in the world and that China's ministry of environmental protection is one of them."

Mr Zhou, an economist and veteran Communist Party member, blamed his ministry's malfunctions on "overlapping" remits, which confused the agency's role in handling issues such as carbon emissions and water monitoring.

The environment minister made no mention of the other three most embarrassing departments but Chinese micro-bloggers were quick to weigh in with their suggestions.

The research paper, published on Tuesday in The Proceedings of the National Academy of Sciences, focuses on the consequences of a 1950-1980 government policy by which free coal was distributed to those living north of the Huai River, which cuts China in two.

While the policy had the "laudable goal of providing indoor heat [it] had disastrous consequences for health," the report says.

As a result of the policy, concentrations of dangerous airborne particles were 55 per cent higher in the north than the south while life expectancies were on average five and a half years lower, the researchers claimed.

"[The study] highlights that in developing countries there's a trade-off in increasing incomes today and protecting public health and environmental quality. And it highlights the fact that the public health costs are larger than we had thought," Michael Greenstone, a Massachusetts Institute of Technology professor in environmental economics and one of the paper's authors, told The New York Times.

Air pollution's role in a number of health problems is no secret. But the new study, which is based on official statistics from 1981 to 2001 and was written by researchers from China, Israel and the United States, lays bare the link between long-term exposure to pollution and increased mortality rates.

The report's authors said their work also helped to explain "why China's explosive economic growth has led to relatively anaemic growth in life expectancy".

Since taking over as the Communist Party chairman last November, Xi Jinping has vowed to tackle pollution head-on.

In May he warned that officials and companies would be punished if they crossed an "ecological red line". "Our environmental protection and rehabilitation efforts should focus on solving obvious issues that harm people's health," he said.